Tone processing system



United States Patent [72] Inventor David A. Bungei' 3,391,240 7/1968Uetrecht 84/l.l9X Cincinnati, Ohio 3,429,976 2/1969 Tomcik 84/ 1.12 [211App]. No. 712,117 Primar "l I y Exammer- Herman k. Saalbach g fs g f rAssistant ExaminerT. Vezeau a Attorneys-W. H. Breunig and Hurvitz, Rose& Greene [73] Assignee D. H. Baldwin Company Cincinnati, Ohio acorporation of ohm ABSTRACT: A tone derived from a conventional musicalin strument, such as a clarinet, is converted to a square wave signalhaving the same fundamental frequency as the funda- [54] TONE PROCESSINGSYSTEM mental frequency of the tone. The square wave signal frequen- 7Claims, 2 Drawing Figs cy is divided by two, and again by two, and isalso multiplied by two-thirds, to provide three waves, each of which maybe [52] US. Cl 84/1-12, processed by tone color filters to have avariety f musical 84/121 84/122 sounds, as the sounds of the oboe, tuba,flute, etc. The original [51] IIILCI Gloh 3/00, tone is detected toprovide a DC gain control signal which Gloh l/oztcloh 1/06 controls theconductivity of a diode gate through which the [50] Field ofSeai'ch84/l.0l, Processed tone passes Conversion to a Square wave Signal isaccomplished by oppositely poled diode peak detectors, each [56]References Cited including a diode and a'capacitor in series with thediode, the capacitors having a common resistive path to ground, so thatUNITED STATES PATENTS charging of one capacitor is always accompanied bydischarg- 2,989,886 /1 1 Mark witZ 84/l.19 ing of the other. Theconversion system is thus capable of 3,213,130 10/1965 C y el /1-1 1responding to alternate half cycles of complex waves, over 21 3,256,3816/1966 Cookerly et a]., 84/].27 very wide range of frequencies, say fromabout 50c.p.s. t0 ""Llfifi ll/l967 Diidek et al. 307/235X about5,000c.p.s

10 ll S 44 g l2 (13 14 AUDIO DlODE L!" L! F/4 INPUT WAVE F/F 2 I mansSHAPER 84 Anna;

TONE F 100 /2 coLoR FILTERS 2 2F 11 2 TC 21f 2/5 F T 5 2 8i Y 0 l7 DET.

19 r18 1,6 I 5 AUDIO DlQDE m; GAT-E Paten tediNov. 10, 1970 Sheet umEwmid . Pwo

INVENTOR v DNHD A. BUNGER ATTORNEYS TONE PROCESSING SYSTEM BACKGROUND OFTHE INVENTION The general procedure of processing tones provided byconventional musical instruments is old. Reference is made to US. Pat.Nos. as follows: Earp, 2,561,349; White, 3,006,228; Hanert, 2,514,490;Cookerly et al., 3,213,180.

The prior art systems lack a suitable device for assuring that thefundamental of a complex musical tone will, for all frequencies and waveshapes, assume reliable control of the system, keeping in mind that waveshapes of tones produced by musical instruments, such asthe clarinet,differ radically among themselves in respect to wave shapes. In the pastit has been usual to roll off frequencies of the tone, so that thefundamental, if initially at least as great as any harmonic of the tone,will assume control of the system. However, many musical tones haveharmonics which far exceed the fundamental in amplitude. In thesecircumstances the output of the system tends to shift at random in thecourse of playing a single note. It is to this problem that the presentsystem primarily addresses itself.

SUMMARY OF THE INVENTION The output of an acousto-electrical transducer,controlled by a musical instrument, is applied to a push-pull diode peakdetector which generates square waves at the frequency of thefundamental of the output of the transducer, for a wide variety of waveshapes and for a wide range of frequencies. The square wave is dividedby two and again by two, and also is multiplied by two-thirds, thirds,followed by division by three, and multiplied by two.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a systemaccording to the invention; and

FIG. 2 is a schematic circuit diagram of a system according to FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, an audio inputsignal, which may be derived from an acousto-electric transduceroperatively associated with a horn, clarinet, guitar, or the like, isapplied to a diode wave shaper 11, which converts the wave to oneresembling a square wave having the same fundamental frequency as doesthe audio input signal. The output of the diode wave shaper drives atransistor flip-flop 12, which provides a square wave at the fundamentalfrequency, but of level amplitude regardless of the amplitude of theaudio signal. The output of flip-flop 12 drives two cascadeddivide-by-two circuits, 13 and 14, a multiply by two circuit and amultiply by circuit, each of which supplies complex signal to an arrayTC of tone color filters, selectable by operation of tabs, notillustrated. The output of array TC proceeds to a diode gate 16 whichcontrols signal level in response to a DC control voltage applied viacontrol lead 17, and which leads to an audio amplifier 18. The latterdrives a loudspeaker 19. It follows that any complex audio tone,regardless of its wave shape, and of fundamental frequency F, canproduce square waves of fundamental frequency F, F/2, 2F, F and anotherof fundamental frequency F/4. These can be processed by tone colorfilters TC to have the tone colors of various instruments, for example,clarinet, oboe, flute, tuba, saxaphone, dulciana.

The output of transducer 10 is detected in smoothing detector 20, whichprovides DC gain control signal on lead 17, so that the level of soundemitted by loudspeaker 19 will follow that of transducer 10, andtherefore of the level provided by the instrument with which thetransducer is associated.

To the outputs of flip-flop 12 is connected a diode frequency doubler21. The latter derives a divide-by-three circuit 22, the output of whichin turn is applied to the array TC of tone color filters. The frequencyF as provided by flip-flop 12, the outputs of divide-by-two circuits 13,14, the output of multiplier 21, and the output of divide-by-threecircuit are applied via separate leads to tone color filters TC.

In FIG. 2, the output of transducer 10 is applied via coupling capacitor30 and base current limiting resistance 31 to the base of NPN transistorT having a grounded emitter. The collector of T is loaded by resistance32, and the resistances 33, 34 serve to bias the base. Capacitor 35provides frequency selective feedback to accentuate response as aninverse function of frequency, i.e. it provides roll off, whichaccentuates the fundamental of a complex wave at the expense of higherpartials.

The amplified audio signal-appearing at point 36 is superposed on a DCvoltage of about l2.V representing DC supply voltage of 22.V less the DCvoltage drop in resistance 32. To the point 36 are directly connectedthe base of diode D and the anode of diode D A DC path exists throughdiodes D,, D, from supply leads S through resistances 40, 41,respectively, nearly one-half of the available voltage being dropped inresistance 40. This implies that the anode of D is at about l2.V, andboth diodes are biased slightly conductive. When the AC signal goespositive it charges capacitor 43 approximately to its own peak level,and this charge is retained during a half a cycle of input wave so thatif the positive half cycle is quite complex, as is usually the case, anydips of level in the course of the positive half cycle do not affect theoutput level at the base of T Similarly when the signal goes negativewith respect to the normal DC level of point 36 diode D chargescapacitor 44, which back-biases the diode D, and prevents transientdrops in level from generating reverse flows through capacitor 44.Charging of capacitor 44 induces discharge capacitor 43, and vice versa.Since transfer of charging function occurs as the input signal wavepasses through zero level, the system can respond to AC waves over awide range of frequencies, say 50 c.p.s. to 5,000 c.p.s. The doublediode, double capacitor detection system may well be denominated apush-pull peak detector, since it responds to alternate polarities of awave to provide a clipped AC output which approximates a square wave.The closeness of the approximation depends, however, on the complexityof the input wave form, Le. the relative amplitudes and phases of itscomponent partials.

D,, 44 is a peak detector, and D 43 is a peak detector, for negative andpositive signals, respectively, capacitors 43, 44 being in series withrespect to diodes D D and the circuit tends to produce a square wave atthe peaks of the input wave form, changing state as the input signalreverses polarity. Current through load resistance 53 is then an ACsignal with respect to the DC bias for transistor T established byresistances 51, 52, 53. Since the load and bias circuits for T and T areidentical, the DC level at point 54 is nearly the same as the DC levelat point 36. T saturates on sufficiently large signals, its outputhaving values extending to 0 and 22.V as the comprising twocross-connected NPN transistors T and T in a configuration which isconventional and hence is not further described. The collector of T itsemitter being grounded, is AC coupled via capacitor 60 to the cathode ofa grounding diode D and to the anode of a series diode D the cathode ofwhich is grounded through resistance 63. The capacitor 60 and resistance63 convert the DC variations of voltage at the collector T to shortpulses, of which only the positive halves pass to junction 61. A similararrangement pertaining to the collector of T involves capacitor 62 anddiodes D and D Diodes D and D together then pass each oscillation ofFF-l, and the pulse frequency at junction 61 is double that supplied byT Essentially 60, 63 is a differentiator which is rendered inoperativeto negatively going pulses by D D and 62, 63 is a furtherdifferentiator.

The pulses available at junction 61 are applied to a divideby-threecircuit 22, in the form of a ring counter of conventional configuration,via a drive amplifier 66 having an NPN transistor T Divide-by-threecircuit 22 employs three cascaded NPN transistors T T T The output ofamplifier 66 is applied jointly to the collectors of the transistors T TT through 2.2 K resistors 70, 71, 72, these being connected back to DCsupply via resistance 73 (820 9). Each collector is connected back tothe base of the preceding transistor, i.e. T to T T to T and T to T andforward via wave shaping circuits 74, 75, 76, respectively, i.e. T toT,, T-, to T and T to T,. The configuration is well known, and sincecircuit values are provided a detailed description of operational modeis dispensed with.

The output of divide-by-three circuit 65 appears directly at thecollector of T and is applied via a voltage divider 80 and lead 81 to anarray of tone color filters TC, selective by tab operated switches (notshown) in a manner widely employed in electronic organs. The output ofthe array of tone color filters TC appears across resistance 82.

The output of FF-l is applied to cascaded flip-flops 13 (FF- 2) and 14(FF-3), arranged to operate as frequency dividers. These, and flip-flop12, individually apply their outputs via leads 100, 83 and 84 to thearray of tone color filters TC. lnterposed between the leads 100, 83 and84 and the filters TC are adjustable voltage dividers 101, 85 and 86,respectively, which serve as volume adjusters. A further adjustablevoltage divider 103, fed by lead 102 connected to the collector oftransistor 66 is also provided and leads to tone color filters TC. Atthe input of the color filters TC can appear one or more of fivesignals, each of which bears a frequency relation to the frequency ofthe output of transducer 10. If we assume that the transducer provides acomplex signal having a fundamental frequency F, the outputs at leads100, 81, 83, 84, 102 are square waves of frequencies F, 2 F/3, F/2, F/4,2F, respectively, and any one or more of these may be selected by tabswitches (not shown).

The tones provided are, however, of preset amplitudes, which are notrelated to the level at which the instrument which energizes transduceris being played, in absence of the following provision. To controlamplitude according to the level called for by transducer 10, the directoutput of transducer 10 is amplified in amplifier 20, comprisingtransistor T and rectified by diodes D D of detector 20, of which Dshunts negative half cycles to ground and D passes positive half cycles.A long time constant load circuit 91 for D is connected between thecathode of D and ground, so that at junction 92 appears a DC voltagehaving a value nearly proportional to the peak value of the output oftransducer 10. Junction 92 is the control point of a diode gate 16composed of back-to-back diodes D D through which passes in series thesignal across resistance 82. Diode gate 16 is nonconductive in absenceof control voltage applied to control point 92, but becomes moreconductive as control voltage increases. The signal passed by gate 16passes to a voltage amplifier 18, including an NPN transistor T and thelatter drives in cascade a power amplifier 18a and loudspeaker 19.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variation of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

Iclaim:

1. In a system for processing the acoustic tonal output of a nonelectricmusical instrument, wherein:

said output is a complex wave;

a transducer for coupling to said instrument and converting saidacoustic tonal output to an electrical signal having a complex waveform;

a push-pull peak rectifier circuit connected to said transducer;

said push-pull peak rectifier including a junction to which is appliedsaid electrical signal;

a first diode having its cathode connected to said junction;

a first capacitor connected to the anode of saiddiode; a load resistanceconnected in cascade with said first capacitor;

a second diode having its anode connected to said junction;

a second capacitor connected to the cathode of said second diode;

means connecting said second capacitor in cascade with said loadresistance; and i a frequency divider coupled to the output of saidpush-pull rectifier circuit.

2. The combination according to claim 1 wherein is provided a transistorcircuit responsive to the voltage across said load resistance andarranged to become alternately nonconductive and saturated as thevoltage across said load resistance changes algebraic sign.

3. The combination according to claim 2 wherein is provided a flip-flophaving a signal control terminal responsive to said transistor clippingcircuit.

4. The combination according to claim 3, wherein is provided:

diode differentiators responsive to all state transitions of saidflip-flop to provide pulses at twice the frequency of operation of saidflip-flop a divide-by-three counter circuit responsive to said pulses;

a tone color filter array responsive to the output of saiddivide-by-three circuit; and

a loudspeaker coupled to the output of said tone color filter array.

5. An audio gain control'circuit, including:

a source of complex audio tone signals of variable mean amplitudes;

a diode amplitude detector responsive to said tone signals for providinga DC signal constantly proportional in amplitude to said mean amplitude;

a diode gate including back-to-back connected diodes with the connectionof said diodes forming a control point;

means responsive to said complex audio tone signals for generatingsquare wave signals of always the same amplitude regardless of theamplitude of said audio tone signals but of a fundamental frequencyobtained by a simple frequency division from the fundamental frequencyof said complex audio tone signals;

means for musically modifying the frequency spectrum of said square wavesignals to provide musical electrical signals;

means applying said musical electrical signals in cascade with said gatethrough said diodes; and

means for applying said DC signal to said control point, said gate beingarranged to be normally nonconductive in absence of said DC signals atsaid control point.

6. The control circuit of claim 5 wherein said means responsive to saidcomplex audio tone signals includes a push-pull rectifier circuitconnected to said source of complex audio tone signal.

7. The control circuit of claim 6 wherein said pushpull rectifierincludes:

a first peak detector responsive only to the positive portions of saidcomplex audio waves;

a second peak detector responsive only to the negative portions of saidcomplex audio waves; and

a common resistive load circuit for said first and second peakdetectors.

